The present invention relates to the field of detection and diagnosis of ovulation in female mammals through the detection of secondary characteristics occurring during or at the time of ovulation, and more particularly to the detection of ovulation by these secondary characteristics as they appear in human females.
There has for many years been a need to detect and diagnose the precise time of ovulation in a given female mammal. It can be of great importance, for example, to pinpoint the time of ovulation to insure that fertilization occurs and that offspring is produced. Alternatively, it may be important for other medical reasons to diagnose ovulation.
Economically, it is of great interest to livestock breeders, particularly cattle breeders, to be able to detect the times of ovulation of the cows in the herd in order to insure that offspring production is maximized. In dairy herds, for example, conventional techniques for determining ovulation result in as many as 50% of the ovulatory cycles of a given cow being undetected by the breeder. Since artificial insemination is now almost exclusively used to produce fertilization, auxiliary means capable of detecting each incidence of ovulation is in great demand.
Heretofore, there has been no simple, inexpensive test by which a doctor or other individual may diagnose the occurrence of ovulation. Since the occurrence of subsequent vaginal bleeding may not be a reliable indicator that ovulation has indeed occurred, and since in many instances it would be desirable to begin treatment for a suspected condition without awaiting the onset of menstruation to determine that ovulation has, in fact, occurred, a need exists for a method to accurately diagnose the occurrence of ovulation at the time of its occurrence during a menstrual cycle.
The occurrence of ovulation can be established with some certainty through various prior art methods. Even though the only irrefutable method of proving ovulation is the occurrence of conception (or occasionally the actual recovery of the egg), several testing techniques are available which may be used to presumptively confirm the occurrence of ovulation. At present, these tests can give a reasonably good indication that ovulation has or is just about to occur, however, each of these tests are subject to certain disadvantages which affect either the practicality or the reliability of these tests.
1. Surgical Techniques
Surgical techniques for detecting ovulation either call for incisions to be made which facilitate the observation of the corpus luteum of the ovary for physical signs of ovulation, or require that attempts be made to recover the ovum from the oviduct. These have not gained widespread acceptance as simple, safe or reliable techniques.
2. Clinical Techniques
Clinical evaluation has often been suggested as a method of detecting the time of ovulation. One such method focuses upon the appearance of pelvic discomfort at the time of expected ovulation. This "mittelschmerz" is thought to be brought about either by distention of the ovary or by peritoneal irritation from bleeding as a result of follicular rupture. Unfortunately, even among those patients who experience monthly "mittelschmerz", the symptom does not appear to be particularly related to the time of ovulation. Similarly, a mucoid vaginal discharge may sometimes be observed which is the result of increasing secretion from the cervix. This discharge may sometimes be noted immediately prior to ovulation and may be observed in conjunction with premenstrual mastalgia, slight edema or tension. While suggesting that ovulation is in fact occurring, the various techniques described above have proved of little value in precisely predicting or detecting the time of ovulation.
Perhaps the most popular and widely used method of detecting and timing ovulation is the graphic recording of the waking temperature at basal conditions. Using this method, an extremely dedicated woman with uniform daily habits can determine the time of ovulation within two days after its occurrence. In recording the basal body temperature, a rise in temperature is commonly associated with the beginning of the luteal phase, but can vary from the actual time of ovulation by as much as 72 hours. A theoretical basal body temperature chart is illustrated in FIG. 1 and actual basal body temperature charts are illustrated in FIGS. 5 and 6 in connection with the examples set forth herein. In view of the fact that a basal body temperature chart determines the time of ovulation within 2 days after its occurrence, this method is not a reliable one for diagnosing ovulation in that, in most if not all instances, ovulation will have passed before a determination of ovulation can be made.
3. Biochemical or Histological Techniques
In more recent years, various biochemical and histological methods have been developed for detection of the approximate time of ovulation. These methods include histological evaluation of epithelial and/or endometrial samplings, the use of differential staining techniques on vaginal desquamate and the measurement of hormonal levels throughout the menstrual cycle.
It has long been known that a normal menstrual cycle is accompanied by certain cyclic variations in the concentrations of certain hormones appearing in the blood. In humans, the preovulatory rise in serum estrogens coupled with a sharp rise in luteinizing hormone (LH) levels as determined by radio-immunoassay of serially drawn blood samples, is perhaps the most accurate indicator of impending ovulation. Ovulation most likely occurs 12-24 hours after maximum LH levels. A subsequent rise and persistent high level of serum progesterone indicates that ovulation has occurred. Since these determinations are expensive and not widely available, other clinical parameters are used to predict the fertile period, and more particularly, ovulation. These rely on various physical, histological and biochemical changes which may be somewhat more easily monitored.
Taking the day of ovulation as day 0 (the point commonly referred to as being "midcycle"), estrogen levels normally begin to rise on approximately day -3. However, in some women, estrogens may be found to rise as early as day -6, or even earlier. This pre-midcycle estrogen rise is followed by a sharp rise in luteinizing hormone, which is generally accepted to trigger ovulation. Shortly after ovulation, on day +2 or day +3, the level of progesterone begins to rise and remains at sustained levels until day +8 or day +10. The theoretical level of estrogens and progesterone are illustrated in FIG. 1 and actual estrogen and LH (luteinizing hormone) levels for different cycles are shown in FIGS. 4, 5 and 6. Data for these hormones for several experimental subjects is reported in connection with the particular examples set forth hereinafter.
As discussed above, in humans, ovulation is preceded by a large rise in serum estrogens which, in turn, is thought to trigger the release of luteinizing hormone (LH) from the pituitary's anterior lobe. This results in a sharp rise in serum levels of this gonadotropin. Ovulation most likely occurs 12-24 hours after maximum LH levels. It has been demonstrated that fluctuations in the concentrations of gonadotropins and steroid sex hormones during the menstrual cycle correlate with periods of marked changes in cytology and secretory activity in the epithelial lining of the genital tract and oral mucosa of young females.
Certain biochemical tests have also been developed for the purpose of pinpointing the time of ovulation. One such test, referred to as the cervical mucous test, has been devised for the purpose of predicting the time of ovulation through the measurement of the concentration of glucose present in the cervical mucus.
Another test is the monitoring of salivary alkaline phosphatase levels which generally appear to parallel plasma estradiol (estrogen) levels. Unfortunately, the presence of alkaline phosphatase shows significant daily variations, not only between individuals but also within any given individual. Furthermore, this alkaline phosphatase test tends to provide its characteristic indication during a period ranging from 1 to 10 days prior to the actual occurrence of ovulation. Due to this uncertainty, this test appears to be unreliable in predicting either the onset of the fertile period or the actual occurrence of ovulation.
Even more recently, in U.S. patent application Ser. No. 519,220, filed Oct. 30, 1974, and Ser. No. 564,348, filed Apr. 2, 1975, various methods are described whereby vaginal secretions are monitored for certain cyclical changes in volatile organic compounds, particularly lactic acid, acetic acid and urea, for the purpose of predicting and/or detecting the time of ovulation. While these methods are reliable and have met with some success, the fact that they are directed to and require the sampling of vaginal secretions may reduce the probability that these methods will quickly gain widespread acceptance in human populations. Theoretical levels of lactic and acetic acid are illustrated in FIG. 1 and actual levels of lactic acid and urea are illustrated in FIGS. 5 and 6.
It may therefore be concluded that while there are many clinical, histological and biochemical methods which are appropriate for use in detecting the time of ovulation, there is still a substantial need for simple, universally acceptable methods for detecting and diagnosing the precise time of ovulation.
4. Prediction of the Fertile Period
It is generally accepted that the maximum survival function of spermatozoa capable of fertilizing an ovum is approximately 3 days following coitus. Although theoretically any coitus prior to ovulation entails a certain risk of pregnancy, as a practical matter, abstinence from sexual intercourse for the three days prior to ovulation is generally considered to be a "safe" period prior to the occurrence of ovulation. It is generally recognized that the ovum is susceptible to fertilization for a matter of hours. In the rabbit or rat, for example, there is a decreased fertility after the 6th hour. It is generally recognized that the human ovum is fertilizable probably for about 12 hours and certainly for no more than 1 day. The human fertile period, then, is made up of no more than 4 days out of the entire menstrual cycle. If it were possible to accurately predict this fertile period, it would theoretically be necessary to either abstain from intercourse or use alternate birth control methods only for that 4 day "fertile period" rather than for the entire menstrual cycle. Heretofore, the only widely used technique for predicting the fertile period of a female has been the method which relies upon basal body temperature determination of ovulation in a plurality of preceding cycles to determine the expected time of ovulation for future cycles. This method is not really directed to ascertaining the precise fertile period for a given cycle, but rather is intended to establish a statistically "dangerous" period during which coitus is likely to produce pregnancy. Since this information is based upon past performance, and since the time of ovulation varies markedly between different individuals as well as between cycles of a given individual, the period for abstinence must be long enough to considerably reduce the possibility of pregnancy.
One method for calculating the period for abstinence which has been suggested is that intercourse be avoided beginning at the time of menses and continuing until a sustained rise in basal body temperature has been observed. Alternatively, a patient may record 12 previous consecutive cycles, noting the longest and shortest cycles experienced during this interval. Since it is generally agreed that menses usually occurs about 14 days after ovulation, it has been suggested that the fertile period in a given cycle is between 18 and 11 days before menstruation. Using this period as the fertile period, the period for abstinence may be calculated by subtracting 11 days from the longest recorded cycle to arrive at the last unsafe day. Since an extremely regular woman would usually have a cycle which varies in length between 20 and 30 days, the shortest period of abstinence would be expected to range from day 8 to day 19, or more than one-third of the total cycle. It has been estimated that only 55% of the naturally occurring menstrual cycles are within the range of 25 to 31 days, and that even the most regular of women may have cycles which vary from 21 to 33 days. Consequently, it may be concluded that the irregularity and extreme length of the required period of abstinence makes the rhythm method based on basal body temperature and statistical prediction unacceptable to all but the most regular and dedicated of women.
Of the various techniques for detecting ovulation which have been considered above, none of these techniques have the practical capability of predicting the onset of ovulation sufficiently in advance to allow the prospective calculation of the period of abstinence. While certain of these tests may occasionally predict ovulation up to 10 days in advance of its occurrence, all of these tests are equally as likely to give no indication of ovulation until after the onset of the fertile period. This irregularity further procludes any possibility that the tests which do predict ovulation in advance could be used to shorten the period of abstinence since their irregularity would result in periods of abstinence which show no better statistical significance than those based upon the natural occurrence of menstruation. The relative failure of the various techniques discussed above to predict the fertile period in advance has led one commentator to conclude:
"The possibility of predicting ovulation by 3-4 days, and thus providing a couple with a period of abstinence no greater than 5 days is intriguing. John Rock, for one, views this approach with some optimism. Should such a method finally be worked out, it would be but another addition, albeit a vital one, to our armamentarium for controlling the population growth of the world. Certainly, in many nations and even among many couples in our own country, much education would be required to convince the male that he should abstain, even for so short an interval as 5 days, and much effort would have to be expended before some males could look upon this as anything but an infringement of their rights as husbands and lovers. It is clear, nevertheless, that if we could find a way to predict ovulation, we would provide a very natural means of family spacing--in fact, the most physiologic means imaginable. Even if it should require somewhat greater effort than the other methods now available, it would be a real boon to many people, regardless of their religious affiliation. It should be kept in mind that even taking a pill once a day requires some effort and intelligence, and certainly the mechanical contrivances now available are, to say the least, inconvenient." ("The Present Status of Rhythm Techniques", Luigi Mastroianni, Jr., M.D., Clinical Obstetrics and Gynecology, Volume 7, No. 3, 1964, pages 874-875).